Pleural Plaques and Asbestos

Pleural plaques are by far the most common indication of significant exposure to asbestos. Characterized by areas of fibrous thickening on the lining of the lungs (pleura) or diaphragm, the condition typically arises 20 to 30 years after asbestos exposure. The plaques can calcify over time, but they do not cause long-term health problems.

Pleural plaques are benign, which means they are not cancerous. Furthermore, they cannot become cancerous over time. In nearly every case, there are no symptoms, but some patients describe pain or an uncomfortable grating sensation as they breathe.

They can develop on both layers of the pleura, a thin membrane that surrounds the lungs and aids in breathing. They most commonly develop on the parietal pleura, which lines the inside of the rib cage, but can also affect the visceral pleura, which lines the lungs. Additionally, they can grow on the diaphragm, the primary muscle used for respiration.

Pleural plaques are almost exclusively caused by exposure to asbestos, but having the condition does not necessarily mean that you will develop a more serious asbestos-related disease like asbestosis or mesothelioma. However, because the presence of plaques suggests a significant past exposure to asbestos, mesothelioma or lung cancer may arise later in life.

Some studies suggest that fibrous thickening of the pleura may increase a patient's risk for developing pleural mesothelioma, but the topic remains controversial. Contradicting studies say that a patient's risk for other asbestos-related conditions is not affected by a diagnosis of pleural plaques. Instead, they argue that doctors should calculate a patient's risk based on the level and duration of asbestos exposure and how much time has passed since the initial exposure.

How Do They Form?

When people are exposed to asbestos, inhaled fibers can accumulate in the lining of the lungs and irritate the lung tissue. However, it is unclear exactly how asbestos fibers cause pleural plaques to develop.

Pleural Macrophages

A leading theory suggests that the fibers cause an immune response that summons special lung cells called pleural macrophages. These cells can trigger a chain of events that leads to fibrosis, in which specialized cells replace normal, healthy lung tissue with scar tissue made up of collagen fibers.

Pleural Plaque Development

Pleural plaques slowly develop and grow as fibrotic scar tissue accumulates. While doctors traditionally believed they did not affect a patient's lung function, recent evidence shows they sometimes cause a minimal decrease in total lung capacity and other measures of lung function.

In 5 to 15 percent of cases, pleural plaques become calcified. As calcium deposits build up in them, the scar tissue hardens. Rarely, calcified pleural plaques can inhibit lung function and cause patients to have trouble breathing.

Asbestos-exposed patients with pleural plaques may also develop pleural thickening, which involves more extensive fibrous thickening. Because pleural thickening affects a larger area, it can prevent the lungs from fully expanding and cause breathlessness.

Risk, Prevalence and Diagnosis

Often, pleural plaques do not show up until decades after exposure to asbestos. Most experts agree the risk is dose dependent, meaning the risk increases with the level of asbestos exposure and time elapsed since first exposure. Despite this relationship, low levels of asbestos exposure can still cause pleural plaques to arise.

Some studies indicate that between 5 and 15 percent of workers exposed to asbestos on the job will develop fibrous thickening of the pleura 20 years after their initial exposure. In two recent studies in France, doctors screened asbestos-exposed workers using computed tomography (CT) scans.

One study identified pleural plaques in 15.9 percent of 5,545 of workers, and the other confirmed a diagnosis in 46.9 percent of 1,011 workers. The average length of time between first exposure and diagnosis was about 40 years in both studies.

Doctors typically diagnose this condition using a chest X-ray or CT scan. Because it rarely causes symptoms, they usually find it incidentally after performing an imaging scan for an unrelated reason.

Discovery Through X-ray

Most incidences are discovered after an X-ray that displays thickened nodular edges resembling a holly leaf. In certain locations, the condition can be difficult to identify via X-ray. Pleural plaques that are calcified appear more pronounced.

Diagnoses With CT Scan

CT scan is the preferred method for diagnosing this condition, as it can identify plaques anywhere in the chest, even if they are not calcified. In 95 to 100 percent of cases, a CT scan can correctly identify patients who have this condition.

When pleural plaques are first discovered, your health care provider will carefully evaluate your history of asbestos exposure and check for other signs of asbestos-related disease. If you are later diagnosed with an asbestos-related disease, your doctor will create a treatment plan unique to you and your diagnosis.

Treatment and Preventing Further Damage

Because pleural plaques are non-cancerous and the majority of patients do not experience a loss in lung function, treatment is not necessary. However, you can prevent further damage by eliminating any pathways of asbestos exposure and quitting smoking. Your doctor can give you advice to help with smoking cessation.

Although this condition may not place you at a higher risk of developing a more serious asbestos-related disease, you should always notify your doctor if you experience symptoms like breathlessness, a persistent cough, chest pain or coughing up blood. If breathing does become an issue, your doctor can perform a variety of treatments and refer you to a specialist.